1. Field of the Invention
This invention relates to shut-off mechanisms for hand-held pneumatic power tools, and more particularly to a safety shut-off for such tools when the related reaction torque absorption mechanism malfunctions.
2. Description of the Prior Art
The resistance encountered by a workpiece driven by a pneumatic-powered motor is commonly termed the reaction torque. In heavy duty, hand-held pneumatic power tools it is usually necessary to incorporate some mechanism either to prevent the reaction torque of the power tool from exceeding a predetermined level, or to absorb the reaction torque. In devices for preventing the reaction torque from exceeding a given level, specific clutch-type mechanisms have been developed for shutting off the fluid to the motor when a predetermined torque value applied to the workpiece is attained.
Many applications of heavy duty, hand-held pneumatic power tools require a high level of torque, and therefore high levels of reaction torque are generated. A so-called "swing-bar" is often employed to absorb these high levels of reaction torque. One end of the swing-bar, usually an elongated rigid bar, is so incorporated into the tool as to receive the reaction torque which occurs when the workpiece encounters resistance to the torque applied by the motor. The other end of the swing-bar is lodged against an immovable surface for preventing revolution of the swing-bar about the tool during the operation of the tool. The swing-bar thereby cooperates with the immovable surface to absorb the reaction torque.
If, during the operation of the tool, the swing-bar is improperly lodged against the immovable surface, or the swing-bar should break, the tool operator is in danger of being struck by the dislodged or broken swing-bar. At the very least, the sudden unrestricted reaction torque may jerk the tool out of the operator's hands. The prior art fails to disclose a satisfactory fail-safe mechanism for instantaneously shutting off the fluid to a hand-held pneumatic tool of the swing-bar type in case the swing-bar fails to function for any reason while torque is being applied to a workpiece.